Adds a renderer that automatically serializes that "autodata" in the stash into a format based on HTTP Accept and Content-Type headers. Also adds a helper called 'parse_autodata' that handles incoming data by Content-Type.

POST data is parsed according to the type in the 'Content-Type' header with the data left in stash->{autodata}. It is also returned by the above call.

If a route leaves data in stash->{autodata}, it is rendered by this handler, which chooses the type with the first acceptable type listed in the Accept header, the Content-Type header, or the default. (By default, the default is application/json, but you can override that too).